A gas turbine engine typically includes a fan section and a core engine section including a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate an exhaust gas flow. The exhaust gas flow expands through the turbine section to drive the compressor and the fan section, and is also accelerated through an exhaust nozzle to generate thrust.
The fan section drives air through a first bypass passage defined about the core engine. High bypass turbine engines include large bypass passages as compared to airflow through the core engine section and are suited for fuel efficient operation. Engines for applications in high speed aircraft include smaller bypass passages and generate more thrust from the core engine section. Fuel efficiency is increased by utilizing the bypass passage to generate thrust. Greater thrust is generated with more flow through the core engine section as relative to the bypass passage. Fuel efficiency is therefore balanced against aircraft thrust requirements and therefore, smaller bypass passages are utilized to provide higher thrust requirements that sacrifice some fuel efficiency.
A variable cycle gas turbine engine can switch between highly fuel efficient operation with an increased amount of bypass airflow and high speed operation with less bypass airflow and more thrust produced from the core engine section through the exhaust nozzle.
Although variable cycle gas turbine engines have improved operational efficiency, turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies.